This invention relates to electron beam fabrication techniques. More particularly, it relates to a method of making such device which enables extremely high resolution electron beam fabrication.
In the known high resolution electron beam fabrication techniques, there is employed a resist which is coated on to the device substrate by conventional techniques such as spinning. Thereafter, an electron beam is applied to the resist to expose the resist in accordance with the pattern which is desired. Such technique has been utilized, for example, wherein it is desired to provide a pattern of narrow metal lines on a substrate.
It has been found that the ultimate resolution, i.e., the minimum line width, for example, that can be obtained in such fabrication processes is limited by electron scattering both in the resist and back out of the substrate. The minimum line width is not determined by the electron beam diameter. In this connection, electrons from the electron beam may penetrate into the substrate to a distance of two or three microns. Since many substrates have a thickness which is effectively infinite as compared to this penetration distance, there are, therefore, produced a large number of backscattered electrons. The latter tend to expose the resist in the areas adjacent to the portion of the resist exposed by the electron beam, with the consequent result that the width of the exposed area on the resist is substantially wider than the diameter of the electron beam. Such backscattering, consequently, has been a limiting factor in the obtaining of high resolution such as the reduction of the width of metal lines which are provided on a substrate in an electron beam fabrication technique. In this connection, about the narrowest width obtainable by known electron beam techniques of metal lines has been about 700A. Devices comprising very high resolution patterns of a material on a substrate find wide application in electronic circuitry and like devices and the substantial improvement of their resolution would be very advantageous in the miniaturization of circuit devices and in devices utilized for research in fundamental phenomena in physics and in engineering.
Accordingly, it is an important object of this invention to provide a method of making a device upon which there can be laid down a high resolution pattern of material including lines having widths substantially smaller than those heretofore producible.